Recently, portable electronic devices such as camcorders, digital still cameras, mobile phones, and notebook computers have been widely used, and it is strongly demanded to reduce the size and weight, and long-life operation in these devices. Therefore, a battery, particularly a secondary battery having small size and light weight and capable of obtaining high energy density has been developed as a power source.
As such a secondary battery, an aluminum secondary battery utilizing precipitation and dissolution of aluminum for charge-discharge reaction is attracting attention. Because aluminum has a relative higher tendency to become ionic, and thus has large quantities of electricity per unit volume obtained due to redox reaction. Accordingly, aluminum is a very promising material as a material forming an electrode or as an electronic charge carrier.
An aluminum secondary battery has an electrolyte containing an aluminum salt and a solvent together with a cathode and an anode. An electrolyte composition functioning as a medium for charge-discharge reaction highly influences a battery performance, and thus has been variously studied.
Specifically, in order to achieve high capacity and long-life operating, alkyl sulfones such as dimethyl sulfone (see, for example, the patent literature 1) are used. In this case, an organic solvent such as a cyclic carbonate, a chain carbonate, a cyclic ether, or a chain ether is used.
Moreover, in order to reduce polarization in discharge, an organohalogen compound such as trimethylphenylammonium chloride is used together with an aluminum salt such as aluminum chloride (see, for example, the patent literatures 2 and 3). In this case, an organic solvent such as 1,2-dichloroethane is used.